Rioters blocked the road to Beirut airport, as dozens of Syrians were kidnapped and their shops vandalised in violence yesterday that triggered orders from Gulf nations for citizens to leave Lebanon immediately.

Saudi Arabia, which is opposed to Syrian President Bashar al-Assad's regime, told its citizens to leave immediately after "clear threats against them," Lebanon's National News Agency said.

The United Arab Emirates issued a similar warning, with Foreign Minister Shaikh Abdullah bin Zayed Al Nahayan tweeting: "Unfortunately, the situation is very dangerous," while Qatar followed suit.

The warnings came as dozens of Syrians were reportedly kidnapped in Beirut, after unverified television reports claimed the Lebanese abducted in Syria in May were killed in yesterday's air strike in the northern town of Aazaz.

According to the Syrian Observatory for Human Rights, seven of the 11 pilgrims were wounded, but none was killed.

"The relatives and neighbours of several Lebanese kidnapped in Syria took to the streets, and started to harass Syrians and vandalise their property in the area," NNA said.

"Some of the attackers vandalised shops, destroyed cars for sale, and kidnapped dozens of Syrians," it said. "The situation has got out of control." Protesters also blocked off the main road linking Lebanon to Syria, an AFP correspondent said.

Lebanon is one of Gulf tourists' favourite destinations during the summer, as they seek to escape their searing hot climate for the cooler Mediterranean climate and the more liberal lifestyle.

But violence in Syria has spilled over into Lebanon, denting the country's already fragile security situation, with cross-border shootings, shelling by the Syrian army, tit-for-tat kidnappings and sectarian clashes between groups which are divided over the revolt.

The United States voiced support for efforts by Lebanese authorities to maintain calm and said it was not following the action taken by Gulf states.